碳青霉烯类耐药肠杆菌科细菌（CRE）对黏菌素耐药使临床陷入彻底无药可用的困境。我们课题组前期的研究发现（JCM,2011,49:4022），4株CRE菌株对黏菌素耐药，但患者并无黏菌素治疗史，提示该菌株对黏菌素天然耐药，其耐药机制亟待明确。本课题拟重点开展以下研究：①采用质谱分析技术对黏菌素天然耐药和敏感株脂多糖成分的结构进行解析，比较不同菌株的脂多糖在结构修饰上的差异，阐明细菌对黏菌素的天然耐药机制。②采用基因定点突变和克隆技术，分析CRE菌株对黏菌素天然耐药的调控机制，RT-PCR相对定量比较黏菌素耐药和敏感株中PmrA基因及其调控子在mRNA表达水平上的差异。③周边序列测序分析PmrA基因的遗传环境，明确黏菌素不同耐药表型菌株的形成机制。通过上述研究为控制黏菌素耐药菌株的流行传播提供理论依据，为开发针对黏菌素耐药菌株引起感染的新抗菌药提供实验依据。

The emergence of colistin-resistant carbapenem-resistant Enterobacteriaceae (CRE) leads to a dilemma of no-drug for selection to treatment for clinician. Our previous study on CRE isolates indicated (JCM,2011,49:4022) that 4 CRE isolates were resistant to colistin but all the patients had no history of colistin using. These 4 isolates may intrinsic resistant to colistin and the resistant mechanism should be identified urgently. This project will evolve intensively following study: ①To compare the difference of lipopolysaccharide structure between colistin intrinsic resistant and susceptible isolates through the analysis of lipopolysaccharide structure modification by mass spectrographic analysis in order to interpret the intrinsic resistant mechanism of CRE isolates to colistin. ②To study on the regulated mechanism of CRE resistant to colistin through gene site-directed mutagenesis and clone technology. Compare the difference of mRNA transcription and expression level of PmrA and its activated genes between colistin-resistant and susceptible isolates by RT-PCR.③Through analysis the inherited environment of PmrA by DNA sequencing technology, understand the formed mechanism of different phenotype strains to colistin。Our studies can provide theoretical background for controlling the spread of colistin-resistant isolates and give a reference for developing new antimicrobial agent for infections due to colistin-resistant isolates.